The Correct Answer and Explanation is:
Here are the calculated answers for each substance, followed by an explanation of the process.
Correct Answers:
- HCl: 4.005 mol
- NaOH: 0.500 mol
- Al₂O₃: 0.250 mol
- NO₂: 1.60 mol
- CaCO₃: 0.150 mol
- CuO: 0.600 mol
- Br₂: 1.202 mol
- MgO: 0.298 mol
- H₂SO₄: 0.10 mol
- HNO₃: 0.10 mol
- KOH: 0.200 mol
- Xe: 0.050 mol
- Fe₂O₃: 0.010 mol
- SiO₂: 0.320 mol
- Mg(OH)₂: 0.153 mol
Explanation
To solve these problems, we convert the given mass of each substance into its equivalent amount in moles. A mole is a standard unit in chemistry that provides a bridge between the mass of a substance and the number of particles it contains. The key to performing this conversion lies in using the substance’s molar mass.
The first step is to calculate the molar mass for each chemical compound. Molar mass, with units of grams per mole ( g/mol ), represents the mass of exactly one mole of a substance. It is determined by summing the atomic masses of all the individual atoms in the chemical formula. These atomic masses are found on the periodic table. For instance, to find the molar mass of sodium hydroxide (NaOH), you would add the atomic mass of sodium (Na, approx. 22.99 g/mol ), oxygen (O, approx. 16.00 g/mol ), and hydrogen (H, approx. 1.01 g/mol ). The total molar mass for NaOH is approximately 40.00 g/mol .
Once the molar mass is known, the second step is to apply the fundamental conversion formula:
moles = mass (g) / molar mass ( g/mol )
For each question, you take the provided mass in grams and divide it by the molar mass you just calculated for that specific substance. This calculation yields the amount of the substance in moles. Finally, it is important to pay attention to significant figures. The final answer should be rounded to match the number of significant figures in the original mass given in the problem, ensuring the precision of the result is consistent with the measurement. This systematic, two-step method allows for the accurate conversion from mass to moles for any chemical.
